Fabrication of wafer-scale nanopatterned sapphire substrate by hybrid nanoimprint lithography

Abstract

A hybrid nanoimprint soft lithography (HNSL) technique was used to fabricate nanopatterned sapphire substrates (NPSSs) for light-emitting diodes (LEDs). HNSL combines the high resolution of nanoimprint lithography (NIL) and the conformal contact of soft lithography. The key component of HNSL is the hybrid mold, which consists of rigid nanopatterns with an anti-adhesion coating on an elastic poly(dimethylsiloxane) support. The mold was used to fabricate nanopatterns on a 2-in. sapphire substrate through a soft UV-NIL system with a double-layer resist, a top UV-curable layer, and an underlying PMMA layer. Nickel dot arrays were formed from the imprinted patterns through a lift-off process and used as the etching mask during the sapphire etching process due to nickel's high etching resistance. A wafer-scale circular-truncated-cone shaped NPSS was achieved by chlorine-based inductively coupled plasma etching. Typical blue LEDs with emission wavelengths of 452 nm were grown by metal-organic chemical vapor deposition on the NPSS and a flat sapphire substrate (FSS), respectively. The integral electroluminescence intensity and light output power of the NPSS LED were enhanced by 57.9% and 43.8%, respectively, compared to the FSS LED. The high uniformity in photoluminescence intensity across the entire NPSS LED wafer indicated good uniformity of nanopatterns fabricated by HNSL. Low cost and availability of the process and the ability to fabricate at the wafer scale make HNSL a promising method for production of NPSSs.